Thermostatic switch



June Z0, 1950 A. J. KERCHER 2,512,529

THRMOSTATIC SWITCH Filed May l2, 1947 2 Sheets-Sheet 1 A'TT ORNEY June 20, 1950 A. J. KERCHER 2,512,529

THERMOSTATIC SWITCH Filed May 12, 1947 2 Sheets-Sheet 2 F'lE-E l N VEN TOR. ,4r/bur J. #era/1er' Patented .l une 20 1950 THERMOSTATIC SWITCH Arthur J. Kercher, Berkeley, Calif., assignor of one-half to William Wesley Hicks, San Francisco, Calif.

Application May 12, 1947, Serial No. 747,497

1 Claim.

This invention relates generally to thermostats for eiecting control of an electrical circuit in accordance with temperature changes in a given medium, in this particular instance, the medium being air. 'It has particular application to devices of this character for use in conventional electric space heaters.

In thermostats of the above character, it has been common to utilize a thermally responsive element, as for example a bimetallic strip, which will iiex in accordance with temperature changes, connected to a movable electrical contact in such a manner as to move the contact in a full open or closed position with respect to a stationary contact and thereby either open or close an electrical circuit.

The chief defect of most devices of the prior type has been that the same has not been quick or snap acting whereupon sparking has resulted between the contact and improper control of the circuit has prevailed.

It is a general object of the present invention to provide a thermostat which will be characterized by positive opening and closing and which willbe relatively sensitive inits operation.

In the past, in connection with electrical circuits in which such thermostats have been employed, it hasbeen customary to incorporate an electrical switch in the circuit. The incorporation of A`such a switch in an electrical system has increased the cost of electrical heaters and made necessary further engineering in connection with their construction.

It is an object of the present invention to provide a thermostat of the above character in which there will be incorporated means `for retaining the movable contact of the thermostat in such a position that the circuit will remain open and cannot be closed by operation of the thermally responsive elements.

Further objects of the invention will appear from the following description in which the preferred embodiment of the invention vhas been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

Figure 1 is a plan view illustrating a thermostat constructed in accordance with the present invention showingthe movable contact in closed position with respect to the stationary contact.

Figure 2 is a plan view illustrating a thermostat constructed in accordance with the present invention and showing the movable contact in open position with respect to the cooperating stationary contact.

Figure 3 is a rear elevational view of the thery mostatshown in Figure 1.

Figure 4 is a side elevational View of the thermostat shown in Figure 1.

Figure 5 is a fragmentary cross-sectional deshown a pair of cooperating electrical contactsl IlI and I2. The stationary contact Il is carried by a suitable conductor I3 which in turn is provided with a post I4 by means of which it may be. placed in communication with a suitable electri-A cal circuit. The movable contact I2 is carried by one end of a lever arm I6, which in turn is connected to temperature responsive elements I1 and I8, to be presently described.

In order to limit movement of contact I2 in open position, a stop in the form of an upstanding member I9 is provided. Members I3 and I9 are mounted upon a base 2| of non-conducting material which in turn is mounted upon base portion IIJ substantially as shown. Since members I3 and I9 are spaced apart upon non-conducting member 2l they are not in direct electrical contact with each other. Member I9 is provided with a post 22 to which suitable connections may be made to an electrical circuit. A ilexible conductor 23 communicates between post v22 and the lever arm I6 whereby post 22 and movable contact I2 are in constant electrical communication. As has previously been pointed out stationary contact I2 and post I4 are likewise in constant electrical communication. Therefore, when movable contact I2 and stationary contact Il are in contact, an electrical circuit is closed. When movable contact I2 and stationary contact II are not in contact, the circuit is open.

Thermal responsive elements I'I and I8 are preferably in the form of bimetallic strips which tend to ex in response to temperature changes. Strips of this character are well known in the art and are generally formed of layers of material having different temperature coeiiicients of expansion. In this instance these strips are preferably formed spirally as shown. One end of strips I1 and I8 is mounted upon similar axles 26 and 21 which are rotatably mounted in suitable openings '28 and 29, in base I 0.

The ends of strips I1 and I8 remote from axles 26 and 21 are arranged so as to be in spaced relationship. The bimetallic layers of these elements are preferably arranged so that each strip tends to uncoil in response to an increase intemperature, and since the elements I1 and I8 are coiled in opposite directions, their ends 3| and 32 likewise move in opposite directions responsive to changes in temperature. Ends 3| and 32 are pro-- vided with transverse grooves 33 and 34 which cooperate with ridges 36 and '.31iupon.a togglemember 38. Member 38 is-fformed ofnonconducting material and entirely surrounds the lower end of lever I6 and is rigidlyconnected therewith, whereby any motion transmitted to member 38 will be transmitted to lever I6; Member 33 is retained in grooves 33 and 34 by frictional engagement therewith.

I have provided means' in=combination with the foregoing, to adjust the; device for eiecting a control over a wide range-fofqtemperatures. This is done by rotatingy the axles '26 and 2'!` and changingfor adjusting the position of ends 3I andf32'of strips Wand I8zwth respect to the base I. Thus, axles 26 and 21 are provided with lever arms 4I and 42. The ends of levers 4I and 42 remote from aXles 26- and 21 are provided with identical projectingportions 43 and 44 which are rotatably. mounted with. respect thereto. A thre'adedmemberi cooperates with both said members 43fand4'4 and'maintains the same in predeterminedspaced relationship. A nut 41 is provided upon member 46 and abuts against member 43thereby preventingv rotation of member 461. once.. the spaced relationship between membersr'43 and44 has been determined. Intermediate' members 43, and` 44 on the threaded member 46' there is a flanged member 48, whose purpose will hereinafterbe described. It is apparent'that upon movementof anged member IIS'inx onedirection orl another, similar movement ofiarmsIII andLIZoccurs-y thereby rotating axles 26 and 21 as has previouslyibeenl described,v to adjustthedevice for effecting vcontrol at any point over` the rangeof. temperatures.:

The. arms 4I and 42 areprovided with similaranotches'i and and; as'Y shown in Figures 1 and'2a.coil `spring l53 engages notch 5I in arm 4&Ifand-notchv 52 in arm 42 thereby urging the same torthepositions generallyas shown in Figure i, the positionxat which lla higher temperature is requiredto open the circuit, or, in other words, tosnap contact. I2 away fromy contactV II.. rlo-'opposethe normal biasing of spring 53 I haveA provided; a crank member 54, as shown, which the ilange'd member 48; Upon rotation'.

of crankmemberA 54, the flanged member and: threaded member 46-are urged to the right as showniri Figure 2 thereby overcoming 'the bias of' lspring 53: and urging arms 4I and 42 to the positioni shown in Figure 2." It will be appreciated that rotation of crank- 54T may be halted atany point between the extremes shown` in Figures l and 2 thereby effectinga control atfanyv point overthe range of temperatures provided betweenthevpositions of the temperaturey responsive elementsfshown in Figures 'Il'v and 2.

`Afs hasy previously beenpointed out I desire to provide a device for locking'the movablefcontact Iinopen position. I- have provided a member 6I which isfmovablymountedupon base III generall?7 'asl shown inv Figures 311 and 41 by meansof a3 75 4 grooved plate 62. Member 6I is provided with arms 63 and 64. As is shown in Figures 1 and 2 arm 64 is adapted to be engaged by hanged member 48. When the flanged member 48- is urged to the position shown in Figure 2, by means of rotation of crank 54, this motion is transmitted to arm 63 which engages the body 38, as is likewise shown in Figure 2. :When vthe arm 63 engages the body 38 as shown in Figure 2y it is obvious that the contact I2 will be urged into cooperative relationship with the contact II by pressure of the temperature responsive elements I1 and ISwhen the pressure exerted by the same issufcient to overcome the pressure of arm 63.

I have so constructed the device that, when the arm 33 is urgedto the position as shown in Figure 2 no change. in temperature would be sufcient to operate members I1 and I8 to overcome the pressure of member 63. In this manner the device is locked against operation and the circuitis `kept open, regardless of temperature variations. Itfwill beobvious therefore that this lock-out deviceobviates the necessity of the insertion oi'a switch at any other point in the circuit; and thatthe handle', which operates the. crankv 54,' operates as both a means effecting the control of the device over a substantial range of temperatures and also'asa means of effecting a lock-out for. effectively,l retaining contact I2 in openposition-.f

4 When Vthedeviceis in operation the member 38 is subjected toa turning torque to rotate the same. in onedirection or the other depending upon theftemperature ofthe bimetallic strips I1 andv it and upon the position of the iianged member 4B. The turning torque is created by the tendency ofends-3I and 32 to move inopposite directions-in-'response to changes ofA temperature inthe strips ITIl and I c., A toggle effect which makes positive movementof contact I2 is pro-l duced by virtue of the normallyY sprung condition ofA thejbimetallic strips I1. andIS whereby theends StrandSZ invgrooves-33 and 34fare normally biased together upon the ridges36 and 31. For a given settingof thel anged member. 48, a certain-temperature variation is required to `,effect movement ofcontact I2 from .openA to closed position or vice versa.y Assumingnowior a given adjustment of'thedev-ice that the temperature of elements- I and-3 Iii' ismidwayA betweeny certain upperl and: lower limits, contact I2 willremain in either;y opellgor closed-position. Furthermore for such conditions the member 38 will move to a dead' centery position when the contacts areopen orgclosed., Therefore as the temperature variesA betweensuchligmits, contact I2 iscausedto move rapidly to; eitherclosed or'open position and the rapidty'of lmovement isf-caused byupsetting the toggle-formedfby; member 33. If for one settingof the member 48, the contacts-will close at a. giventemperature,- resetting member 48 to change theangular positionofv arms-4I and 42A with:respect=to-the'member 38,- will'require a differentv temperature of strips I1 land I8 to close the contacts. Thus,- by varying the-setting-of theA member 48, the contacts can be --caused to close for: any desired-temperature overa I substantial range; 1

As shown in'Iiiguresandi'y my thermostatic switch Yis adaptedtofbe` placed in an electric air heater, for. example,iof the'itype shown in United States. Letters Patenti 15104379'. Itlwillbe noted that inithis installation'ithe'switch,is adapted to be placed in the incoming air stream y.before the air is heated by the heater. Heaters 'offtliistype are adapted to be mounted either in the wall, near the iloor, or, in the case of portable heaters, are adapted to be placed fairly close to the floor. Cold air is drawn in from the floor and passes over my thermostatic switch before being acted upon by the heating elements. When the cold air drawn in from the iloor reaches a predetermined temperature sulicient to operate members I'I and I8, the switch will be actuated and the circuit broken. As has previously been described rotation of handle 66 operates crank 54 and effects the control of the thermostatic switch over a substantial range of temperatures and also effects a lock-out for eiectively retaining contact I 2 in open position. When the device acts as a lock-out the circuit is kept open regardless of the temperature of the cold air passing over the temperature responsive elements I1 and I8. However when the device does not effect a lockout by retaining contact I2 in open position, the device may be actuated by the effect of the air passing over the strips I1 and I8 as has previously been described.

I claim:

In an electric heater, an electrical heating ele ment for producing heat by convection currents of air and means for controlling said element in accordance with the temperature of the air that is to be acted upon by the heating element, said means comprising a thermostatic switch having a stationary contact and a cooperating contact movable to open and closed position relative to the stationary contact, said cooperating contact adapted to be actuated by a pair of temperature responsive strips in the air stream of the air that is to be acted upon by the heater, means associated with said strips to determine the temperature at which they actuate said movable contact, a handle for positioning said means, and a lockout means adapted to prevent movement o! said movable contact from full open position, said lockout means also being adapted to be operated by said handle for positioning said means to determine the temperature at which said strips actuate said movable contact.

ARTHUR J. KERCHER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,704,479 Kercher et al. Mar. 5, 1929 1,839,935 Thomas Jan. 5, 1932 

